Slow start circuit based on BUCK converter

Abstract

The invention provides a slow power-on circuit for a servo system. The slow power-on circuit comprises a control power supply module, a BUCK converter module, a PWM generator module, a state display module and a totem pole driving module. A BUCK converter is connected in series between main power loops, the magnitude of surge current is determined by the peak value of inductive current, and the increase of voltage on a capacitor is realized by controlling the duty ratio of an MOSFET (Metal-Oxide-Semiconductor Field Effect Transistor). The high-frequency inductor is adopted to suppress surge current, so that space is saved, and the energy utilization rate is increased; the voltage at the two ends of the load capacitor is gradually increased by adopting a method for adjusting the duty ratio to be gradually increased, and universality is achieved; the peak value of the input current is effectively reduced in a duty ratio chopping mode, and the time required by the slow power-on process is shortened; whether a fault occurs in the slow power-on process or not is judged according to the light emitting condition of the light-emitting diode.

Description

Technical Field

[0001] The invention belongs to the technical field of power supply and distribution, and in particular relates to a soft start circuit based on a BUCK converter. Background Art

[0002] In the servo system, in order to suppress the surge current generated by the charging of the DC bus capacitor, a slow start circuit is used. The usual circuit structure is in the form of a resistor in parallel with a relay. Although the resistor in series with the main circuit can realize the current limiting function, it has the following problems: First, since the resistor body needs to bear all the pulse energy, and the energy time width is short and the peak value is large, it is difficult for the resistor body to conduct the heat away in a short time. Therefore, in high-voltage and high-power applications, the volume and power of the resistor are selected with a large margin; second, the surge current is determined by the resistance value and the input voltage. If you want to get a smaller surge current, you can only increase the resistance value, which will lead to a longer slow start time; third, the slow power-on timing is: close the relay after the DC bus capacitor is fully charged, and the driver can only work under load after the relay is closed. If a load starting condition occurs, the resistor is very likely to explode due to overpower; fourth, the action of the relay contacts will cause electromagnetic interference.

[0003] For example, patent CN115425833, named as a power supply slow start circuit, extends the MOSFET turn-on time by utilizing the Maitreya effect during the MOSFET turn-on process (i.e., the gate-source voltage has a Maitreya platform, the VGS voltage remains unchanged, and the VDS gradually decreases), and then the voltage across the output capacitor slowly rises to the power supply voltage along with the Maitreya effect. Although this method can achieve a slow rise in capacitor voltage, the VGS voltage corresponding to the Maitreya platform of the MOSFET requires multiple tests to obtain, and its size is determined by the characteristics of the MOSFET and stray inductance, which is difficult to quantify. Therefore, the content disclosed in this patent is not universal. Summary of the invention

[0004] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a slow power-on circuit for a servo system, in which a BUCK converter is connected in series between the main power circuits, the size of the surge current is determined by the peak value of the inductor current, and the increase in the voltage on the capacitor is achieved by controlling the duty cycle of the MOSFET.

[0005] A slow power-on circuit for a servo system comprises: a control power supply module, a BUCK converter module, a PWM generator module, a state display module and a totem pole driving module.

[0006] After the DC power supply DC is powered on, the output of the control power module supplies power to the PWM generator module, the status display module and the totem pole module; the PWM generator module outputs a PWM square wave with a gradually increasing duty cycle under the condition that the control power meets the requirements, and the PWM square wave controls the BUCK converter module to adjust the voltage after the totem pole drive module increases the driving capacity; as the duty cycle gradually increases from zero to one, the input voltage of the servo driver gradually increases from zero to the DC power supply voltage.

[0007] Preferably, the control power module includes a resistor R5, a Zener diode ZD1 and a capacitor C5, one end of the resistor R5 is connected to the positive electrode of the DC power supply DC, the other end of the resistor R5 is connected to the cathode of the Zener diode ZD1, the anode of the Zener diode ZD1 is grounded, the capacitor C5 is connected in parallel with the Zener diode ZD1, and the cathode of the Zener diode ZD1 serves as the output end of the control power module.

[0008] Preferably, the PWM generator module includes a resistor R4, a capacitor C4, a resistor R3, a capacitor C2, a voltage regulator ZD2, a charging resistor R1, a charging diode D1, a discharging resistor R2, a discharging diode D2, a charging and discharging capacitor C1 and a 555 timer; the output of the control power module can be divided into two paths, one path is connected to one end of the resistor R4, and the other path is connected to one end of the resistor R3, and the resistance value of the resistor R4 is greater than the resistance value of the resistor R3. The other end of the resistor R4 is respectively connected to one end of the capacitor C4 and the VCC pin of the 555 timer, and the other end of the capacitor C4 is connected to the ground, and the capacity of the capacitor C4 is much greater than the capacity of the capacitor C2; the other end of the resistor R3 is connected to the cathode of the voltage regulator diode ZD2, and the anode of the voltage regulator diode ZD2 is connected to the ground, and the breakdown voltage of the voltage regulator diode ZD2 is less than The capacitor C2 is connected in parallel with the voltage zener diode ZD2; the cathode of the diode ZD2 is connected to one end of the charging resistor R1, the other end of the charging resistor R1 is connected to the anode of the charging diode D1, and the cathode of the charging diode D1 is grounded through the charging and discharging capacitor C1; the other end of the charging resistor R1 is also connected to one end of the discharging resistor R2, the other end of the discharging resistor R2 is connected to the cathode of the discharging diode D2, the cathode of the discharging diode D2 is connected to the TH pin and TR' pin of the 555 timer at the same time, and the anode of the discharging diode D2 is grounded through the charging and discharging capacitor C1. The VO pin of the 555 timer outputs a PWM square wave, and the GND pin of the 555 timer is connected to the ground of the DC power supply DC.

[0009] Preferably, the status display module includes a current limiting resistor R6 and a light emitting diode D4, one end of the current limiting resistor R6 is connected to the VCC pin of the 555 timer, the other end of the current limiting resistor R6 is connected to the cathode of the light emitting diode D4, and the anode of the light emitting diode is grounded.

[0010] Preferably, the totem pole driving module includes an NPN transistor Q2 and a PNP transistor Q3, the bases of the transistor Q2 and the transistor Q3 are connected together and controlled by a square wave output by a PWM generator; the collector of the transistor Q2 is connected to the VCC pin of the 555 timer, the emitter of the transistor Q2 and the emitter of the transistor Q3 are connected together as the output end of the totem pole driving module, and the collector of the transistor Q3 is grounded.

[0011] Preferably, the BUCK converter module includes a MOSFET switch tube Q1, a freewheeling diode D3, an inductor L1 and a load capacitor C3. The source of the MOSFET switch tube is grounded, the drain of the MOSFET switch tube is connected to one end of the inductor L1, and the gate of the MOSFET is connected to the output end of the totem pole drive module; the other end of the inductor L1 is connected to one end of the load capacitor C3, and the other end of the load capacitor is connected to the cathode of the freewheeling diode D3, the cathode of the freewheeling diode D3 is connected to the positive electrode of the DC power supply DC, the anode of the freewheeling diode is connected to the drain of the MOSFET, and the servo driver is connected in parallel with the load capacitor C3.

[0012] The beneficial effects of the present invention are as follows:

[0013] (1) Compared with the existing technology that uses a main circuit series resistor to suppress surge current, the present invention uses a high-frequency inductor to suppress surge current, which can not only save space (the volume of the inductor decreases with the increase of the operating frequency, and the inductor has a strong short-term overcurrent capacity), but also effectively improve energy utilization (the resistor suppresses the surge current by consuming energy, and the inductor suppresses the surge current by the nature of its magnetic properties, and the energy is ultimately transferred to the load capacitor). In addition, after the slow power-on is completed, since the inductor is connected in series between the main circuits, it is beneficial to reduce differential mode interference and improve the electromagnetic compatibility of the system.

[0014] (2) The present invention achieves the purpose of gradually increasing the voltage across the load capacitor by using a method of gradually increasing the duty cycle. Compared with the existing technology that uses delayed MOSFET opening time to adjust the output voltage, the duty cycle adjustment is not only not subject to the characteristics of the switch tube and the influence of stray inductance, but also the voltage across the load capacitor is linearly related to the input DC power supply voltage (i.e., VO / VI=D), so it has universal applicability.

[0015] (3) The present invention controls the magnitude of the inductor current by adjusting the duty cycle. As the duty cycle gradually increases, the average current flowing through the inductor also increases, which means that the voltage on the load capacitor also gradually increases. Compared with the resistor current limiting or switch current limiting measures adopted in the existing technology, the present invention divides the peak value and time of the input current into multiple small pulses by duty cycle chopping, which not only effectively reduces the peak value of the input current, but also further reduces the time required for the slow power-on process.

[0016] (4) The present invention obtains control power by taking power from an input DC power supply, thereby solving the problem that a high-voltage input DC power supply cannot directly supply control power and a separate DC / DC power converter for converting high voltage to low voltage is required. This not only saves circuit costs, but also, because the circuit structure of the control power module is simple and highly portable, it can also be used in other self-sufficient power supply circuits that take power from a DC bus.

[0017] (5) The present invention observes the slow power-on completion status through the status display module. After the power supply end of the PWM generator module reaches the maximum threshold, the light-emitting diode lights up, indicating that the slow power-on process has been completed. If the light-emitting diode does not light up after the DC power supply is powered on, it means that a fault has occurred in the slow power-on process. At this time, the servo driver cannot work normally. This circuit is not only simple and practical, but also intuitive.

[0018] (6) The present invention connects the source of the MOSFET switch tube in the BUCK converter to the ground and the drain of the MOSFET switch tube to the inductor, thereby connecting the source of the MOSFET switch tube to the control ground. This not only reduces the isolation circuit of the MOSFET floating ground drive in the traditional BUCK converter, but also improves the anti-interference ability of the MOSFET drive circuit, thereby increasing the reliability of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 The present invention is a schematic diagram of a slow power-on circuit based on a BUCK converter. DETAILED DESCRIPTION

[0020] like Figure 1 A slow power-on circuit for a servo system shown includes: a control power supply module, a BUCK converter module, a PWM generator module, a state display module and a totem pole drive module.

[0021] After the DC power supply DC is powered on, the output of the control power module supplies power to the PWM generator module, the status display module and the totem pole module; the PWM generator module outputs a PWM square wave with a gradually increasing duty cycle under the condition that the control power meets the requirements, and the PWM square wave controls the BUCK converter module to adjust the voltage after the totem pole drive module increases the driving capacity; as the duty cycle gradually increases from zero to one, the input voltage of the servo driver gradually increases from zero to the DC power supply voltage.

[0022] Preferably, the control power module includes a resistor R5, a Zener diode ZD1 and a capacitor C5, one end of the resistor R5 is connected to the positive electrode of the DC power supply DC, the other end of the resistor R5 is connected to the cathode of the Zener diode ZD1, the anode of the Zener diode ZD1 is grounded, the capacitor C5 is connected in parallel with the Zener diode ZD1, and the cathode of the Zener diode ZD1 serves as the output end of the control power module.

[0023] Preferably, the PWM generator module includes a resistor R4, a capacitor C4, a resistor R3, a capacitor C2, a voltage regulator ZD2, a charging resistor R1, a charging diode D1, a discharging resistor R2, a discharging diode D2, a charging and discharging capacitor C1 and a 555 timer; the output of the control power module can be divided into two paths, one path is connected to one end of the resistor R4, and the other path is connected to one end of the resistor R3, and the resistance value of the resistor R4 is greater than the resistance value of the resistor R3. The other end of the resistor R4 is respectively connected to one end of the capacitor C4 and the VCC pin of the 555 timer, and the other end of the capacitor C4 is connected to the ground, and the capacity of the capacitor C4 is much greater than the capacity of the capacitor C2; the other end of the resistor R3 is connected to the cathode of the voltage regulator diode ZD2, and the anode of the voltage regulator diode ZD2 is connected to the ground, and the breakdown voltage of the voltage regulator diode ZD2 is less than The capacitor C2 is connected in parallel with the voltage zener diode ZD2; the cathode of the diode ZD2 is connected to one end of the charging resistor R1, the other end of the charging resistor R1 is connected to the anode of the charging diode D1, and the cathode of the charging diode D1 is grounded through the charging and discharging capacitor C1; the other end of the charging resistor R1 is also connected to one end of the discharging resistor R2, the other end of the discharging resistor R2 is connected to the cathode of the discharging diode D2, the cathode of the discharging diode D2 is connected to the TH pin and TR' pin of the 555 timer at the same time, and the anode of the discharging diode D2 is grounded through the charging and discharging capacitor C1. The VO pin of the 555 timer outputs a PWM square wave, and the GND pin of the 555 timer is connected to the ground of the DC power supply DC.

[0024] Preferably, the status display module includes a current limiting resistor R6 and a light emitting diode D4, one end of the current limiting resistor R6 is connected to the VCC pin of the 555 timer, the other end of the current limiting resistor R6 is connected to the cathode of the light emitting diode D4, and the anode of the light emitting diode is grounded.

[0025] Preferably, the totem pole driving module includes an NPN transistor Q2 and a PNP transistor Q3, the bases of the transistor Q2 and the transistor Q3 are connected together and controlled by a square wave output by a PWM generator; the collector of the transistor Q2 is connected to the VCC pin of the 555 timer, the emitter of the transistor Q2 and the emitter of the transistor Q3 are connected together as the output end of the totem pole driving module, and the collector of the transistor Q3 is grounded.

[0026] Preferably, the BUCK converter module includes a MOSFET switch tube Q1, a freewheeling diode D3, an inductor L1 and a load capacitor C3. The source of the MOSFET switch tube is grounded, the drain of the MOSFET switch tube is connected to one end of the inductor L1, and the gate of the MOSFET is connected to the output end of the totem pole drive module; the other end of the inductor L1 is connected to one end of the load capacitor C3, and the other end of the load capacitor is connected to the cathode of the freewheeling diode D3, the cathode of the freewheeling diode D3 is connected to the positive electrode of the DC power supply DC, the anode of the freewheeling diode is connected to the drain of the MOSFET, and the servo driver is connected in parallel with the load capacitor C3.

Claims

1. A slow power-on circuit for a servo system, include: A control power module, a BUCK converter module, a PWM generator module, a status display module and a totem pole drive module, wherein the control power module supplies power to other modules after the DC power supply DC is powered on, and the PWM generator module outputs a PWM square wave with a gradually increasing duty cycle under the condition that the control power meets the requirements. The PWM square wave controls the BUCK converter module to adjust the voltage after the driving capability is increased by the totem pole drive module. As the duty cycle gradually increases from zero to one, the input voltage of the servo driver gradually increases from zero to the DC power supply voltage.

2. According to claim 1, a slow power-on circuit for a servo system, the control power module includes a resistor R5, a Zener diode ZD1 and a capacitor C5, one end of the resistor R5 is connected to the positive electrode of the DC power supply DC, the other end of the resistor R5 is connected to the cathode of the Zener diode ZD1, the anode of the Zener diode ZD1 is grounded, the capacitor C5 is connected in parallel with the Zener diode ZD1, and the cathode of the Zener diode ZD1 serves as the output end of the control power module.

3. According to the slow power-on circuit for a servo system as described in claim 1, the PWM generator module includes a resistor R4, a capacitor C4, a resistor R3, a capacitor C2, a voltage regulator ZD2, a charging resistor R1, a charging diode D1, a discharging resistor R2, a discharging diode D2, a charging and discharging capacitor C1 and a 555 timer.

4. According to the slow power-on circuit for a servo system as described in claim 3, the output of the control power module can be divided into two paths, one path is connected to one end of the resistor R4, and the other path is connected to one end of the resistor R3, and the resistance value of the resistor R4 is greater than the resistance value of the resistor R3.

5. According to a slow power-on circuit for a servo system as described in claim 3-4, the status display module includes a current limiting resistor R6 and a light-emitting diode D4, one end of the current limiting resistor R6 is connected to the VCC pin of the 555 timer, and the other end of the current limiting resistor R6 is connected to the cathode of the light-emitting diode D4, and the anode of the light-emitting diode is grounded.

6. According to the slow power-on circuit for a servo system as described in claim 5, after the power supply end of the PWM generator module reaches the maximum threshold, the light-emitting diode D4 lights up, indicating that the slow power-on process has been completed; if the light-emitting diode D4 is not lit after the DC power supply is powered on, it means that a fault has occurred in the slow power-on process, and the servo driver cannot work normally at this time.

7. According to a slow power-on circuit for a servo system as described in claims 3-6, the totem pole driving module includes an NPN transistor Q2 and a PNP transistor Q3, the bases of the transistor Q2 and the transistor Q3 are connected together and controlled by the square wave output of the PWM generator; the collector of the transistor Q2 is connected to the VCC pin of the 555 timer, the emitter of the transistor Q2 and the emitter of the transistor Q3 are connected together as the output end of the totem pole driving module, and the collector of the transistor Q3 is grounded.

8. A slow power-on circuit for a servo system according to claims 1-7, wherein the BUCK converter module comprises a MOSFET switch tube Q1, a freewheeling diode D3, an inductor L1 and a load capacitor C3. 9 . The slow power-on circuit for a servo system according to claim 8 , wherein the source of the MOSFET switch tube Q1 is grounded, and the drain is connected to the inductor L1 .

10. According to the slow power-on circuit for a servo system as described in claim 9, the gate of the MOSFET is connected to the output end of the totem pole driving module; the other end of the inductor L1 is connected to one end of the load capacitor C3, the other end of the load capacitor C3 is connected to the cathode of the freewheeling diode D3, the cathode of the freewheeling diode D3 is connected to the positive electrode of the DC power supply DC, the anode of the freewheeling diode is connected to the drain of the MOSFET, and the servo driver is connected in parallel with the load capacitor C3.

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